Showing papers by "Alberto Santoro published in 2001"

Experimental evidence for a light and broad scalar resonance in D(+) --> pi(-)pi(+)pi(+) decay.

Abstract: From a sample of 1172 +/- 61 D(+)-->pi(-)pi(+)pi(+) decays, we find gamma(D(+)-->pi(-)pi(+)pi(+))/gamma(D(+)-->K-pi(+)pi(+)) = 0.0311 +/- 0.0018(+0.0016)(-0.0026). Using a coherent amplitude analysis to fit the Dalitz plot of these decays, we find strong evidence that a scalar resonance of mass 478(+24)(-23) +/- 17 MeV/c(2) and width 324(+42)(-40) +/- 21 MeV/c(2) accounts for approximately half of all decays.

Study of the D(+)(s)-->pi(-)pi(+)pi(+) decay and measurement of f(0) masses and widths.

Abstract: From a sample of $848\ifmmode\pm\else\textpm\fi{}44$ ${D}_{s}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}$ decays, we find $\ensuremath{\Gamma}({D}_{s}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+})/\ensuremath{\Gamma}({D}_{s}^{+}\ensuremath{\rightarrow}\ensuremath{\varphi}{\ensuremath{\pi}}^{+})\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.245\ifmmode\pm\else\textpm\fi{}{0.028}_{\ensuremath{-}0.012}^{+0.019}$. Using a Dalitz plot analysis of this three body decay, we find significant contributions from the channels ${\ensuremath{\rho}}^{0}(770){\ensuremath{\pi}}^{+}$, ${\ensuremath{\rho}}^{0}(1450){\ensuremath{\pi}}^{+}$, ${f}_{0}(980){\ensuremath{\pi}}^{+}$, ${f}_{2}(1270){\ensuremath{\pi}}^{+}$, and ${f}_{0}(1370){\ensuremath{\pi}}^{+}$. We also present the values obtained for masses and widths of the resonances ${f}_{0}(980)$ and ${f}_{0}(1370)$.

Direct measurement of the pion valence quark momentum distribution, the pion light-cone wave function squared

Abstract: We present the first direct measurements of the pion valence-quark momentum distribution which is related to the square of the pion light-cone wave function. The measurements were carried out using data on diffractive dissociation of 500 GeV/c pi(-) into dijets from a platinum target at Fermilab experiment E791. The results show that the /q&q> light-cone asymptotic wave function describes the data well for Q2 approximately 10 (GeV/c)(2) or more. We also measured the transverse momentum distribution of the diffractive dijets.

Observation of color-transparency in diffractive dissociation of pions

Abstract: We have studied the diffractive dissociation into di-jets of 500 GeV/c pions scattering coherently from carbon and platinum targets. Extrapolating to asymptotically high energies (where t_{min} approaches 0) we find that when the per-nucleus cross-section for this process is parameterized as $ \sigma = \sigma_0 A^{\alpha} $, $ \alpha $ has values near 1.6, the exact result depending on jet transverse momentum. These values are in agreement with those predicted by theoretical calculations of color-transparency.

Search for Large Extra Dimensions in Dielectron and Diphoton Production

Abstract: We report a search for effects of large extra spatial dimensions in ppbar collisions at a center-of-mass energy of 1.8 TeV with the DZero detector, using events containing a pair of electrons or photons. The data are in good agreement with the expected background and do not exhibit evidence for large extra dimensions. We set the most restrictive lower limits to date, at the 95% confidence level, on the effective Planck scale between 1.0 TeV and 1.4 TeV for several formalisms and numbers of extra dimensions.

High-[Formula Presented] jets in [Formula Presented] collisions at [Formula Presented] and 1800 GeV

Abstract: Results are presented from analyses of jet data produced in pp collisions at √s=630 and 1800 GeV collected with the DO detector during the 1994–1995 Fermilab Tevatron Collider run. We discuss the details of detector calibration, and jet selection criteria in measurements of various jet production cross sections at √s=630 and 1800 GeV. The inclusive jet cross sections, the dijet mass spectrum, the dijet angular distributions, and the ratio of inclusive jet cross sections at √s=630 and 1800 GeV are compared to next-to-leading-order QCD predictions. The order αs3 calculations are in good agreement with the data. We also use the data at √s=1800 GeV to rule out models of quark compositeness with a contact interaction scale less than 2.2 TeV at the 95% confidence level.

Quasi-model-independent search for new physics at large transverse momentum

Abstract: We apply a quasi-model-independent strategy ("SLEUTH") to search for new high p(T) physics in approximate to 100 pb(-1) of p (p) over bar collisions at roots = 1.8 TeV collected by the D empty set experiment during 1992-1996 at thr Fermilab Tevatron. Over 32 e muX, W+jets-like, Z+jets-like, and (ll gamma)(ll gamma)(ll gamma )X exclusive final states are systematically analyzed for hints of physics beyond the standard model. Simultaneous sensitivity to a variety of models predicting new phenomena at the electroweak scale is demonstrated by testing the method on a particular signature in each set of final states. No evidence of new high p(T) physics is observed in the course of this search, and we find that 89% of an ensemble of hypothetical similar experimental runs would have produced a final state with a candidate signal more interesting than the most interesting observed in these data.

High-pTjets inp¯pcollisions ats=630and 1800 GeV

Abstract: Results are presented from analyses of jet data produced in $p\overline{p}$ collisions at $\sqrt{s}=630$ and 1800 GeV collected with the D\O{} detector during the 1994--1995 Fermilab Tevatron Collider run We discuss the details of detector calibration, and jet selection criteria in measurements of various jet production cross sections at $\sqrt{s}=630$ and 1800 GeV The inclusive jet cross sections, the dijet mass spectrum, the dijet angular distributions, and the ratio of inclusive jet cross sections at $\sqrt{s}=630$ and 1800 GeV are compared to next-to-leading-order QCD predictions The order ${\ensuremath{\alpha}}_{\mathrm{s}}^{3}$ calculations are in good agreement with the data We also use the data at $\sqrt{s}=1800$ GeV to rule out models of quark compositeness with a contact interaction scale less than $22$ TeV at the $95%$ confidence level

Inclusive Jet Production in pp̅ Collisions

Abstract: We report a new measurement of the pseudorapidity (eta) and transverse-energy (Et) dependence of the inclusive jet production cross section in pbar b collisions at sqrt(s) = 1.8 TeV using 95 pb**-1 of data collected with the DZero detector at the Fermilab Tevatron. The differential cross section d^2sigma/dEt deta is presented up to |eta| = 3, significantly extending previous measurements. The results are in good overall agreement with next-to-leading order predictions from QCD and indicate a preference for certain parton distribution functions.

Search for rare and forbidden Charm Meson decays D0 --> Vl+l- and hhll.

Abstract: We report results of a search for flavor-changing neutral current (FCNC), lepton flavor, and lepton-number violating decays of the ${D}^{0}$ (and its antiparticle) into three and four bodies. Using data from Fermilab charm hadroproduction experiment E791, we examine modes with two leptons (muons or electrons) and a ${\ensuremath{\rho}}^{0}$, ${\overline{K}}^{*0}$, or $\ensuremath{\varphi}$ vector meson or a nonresonant $\ensuremath{\pi}\ensuremath{\pi}$, $K\ensuremath{\pi}$, or $\mathrm{KK}$ pair of pseudoscalar mesons. No evidence for any of these decays is found. Therefore, we present branching-fraction upper limits at 90% confidence level for the 27 decay modes examined (18 new).

Ratio of isolated photon cross sections in p(p)over-bar collisions at root s=630 and 1800 GeV

Abstract: The inclusive cross section for production of isolated photons has been measured in p (p) over bar collisions at roots = 630 GeV with the DO detector at the Fermilab Tevatron Collider. The photons span a transverse energy (E-T) range from 7-49 GeV and have pseudorapidity \eta\ s = 1800 GeV to form a ratio of the cross sections. Comparison of next-to-leading-order QCD with the measured cross section at 630 GeV and the ratio of cross sections show satisfactory agreement in most of the E-T range.

Search for heavy particles decaying into electron-positron pairs in pp collisions.

Abstract: We present results of searches for technirho (rho (T)), techniomega (omega (T)), and Z' particles, using the decay channels rho (T), omega (T), Z' --> e(+)e(-). The search is based on 124.8 pb(-1) of data collected by the DO detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes p (p) over bar --> rho (T), omega (T), Z' - e(+)e(-) as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate rho (T) and omega (T) states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson.

Search for new physics using QUAERO: a general interface to D0 event data

Abstract: We describe Quaero, a method that i) enables the automatic optimization of searches for physics beyond the standard model, and ii) provides a mechanism for making high energy collider data generally available. We apply Quaero to searches for standard model WW, ZZ, and ttbar production, and to searches for these objects produced through a new heavy resonance. Through this interface, we make three data sets collected by the D0 experiment at sqrt(s)=1.8 TeV publicly available.

Search for First-Generation Scalar and Vector Leptoquarks

Abstract: We describe a search for the pair production of first-generation scalar and vector leptoquarks in the eejj and evjj channels by the DO Collaboration. The data are from the 1992-1996 p (p) over bar run at roots = 1.8 TeV at the Fermilab Tevatron collider. We find no evidence for leptoquark production: in addition. no kinematically interesting events are observed using relaxed selection criteria. The results from the eejj and evjj channels are combined with those from a previous DO analysis of the vvjj channel to obtain 95% confidence level (C.L.) upper limits on the leptoquark pair-production cross section as a function of mass and of beta. the branching fraction to a charged lepton. These limits are compared to next-to-leading-order theory to set 95% C.L. lower limits on the mass of a first-generation scalar leptoquark of 225, 204, and 79 GeV/c(2) for beta = 1. 1/2. and 0, respectively. For vector leptoquarks with gauge (Yang-Mills) couplings, 95% C.L. lower limits of 345. 337, and 206 GeV/c(2) are set on the mass for beta = 1, 1/2, and 0. respectively. Mass limits for vector leptoquarks are also set for anomalous vector couplings.

Ratio of Jet Cross Sections at √s= 630 GeV and 1800 GeV

Abstract: The D0 Collaboration has measured the inclusive jet cross section in barpp collisions at square root of s = 630 GeV. The results for pseudorapidities (eta)<0.5 are combined with our previous results at square root of s = 1800 GeV to form a ratio of cross sections with smaller uncertainties than either individual measurement. Next-to-leading-order QCD predictions show excellent agreement with the measurement at 630 GeV; agreement is also satisfactory for the ratio. Specifically, despite a 10% to 15% difference in the absolute magnitude, the dependence of the ratio on jet transverse momentum is very similar for data and theory.

Search for dilepton signatures from minimal low-energy supergravity in pp̄ collisions at √s = 1.8 TeV

Abstract: We report on a search for supersymmetry using the D\O{} detector. The 1994--1996 data sample of $\sqrt{s}=1.8$ TeV $p\overline{p}$ collisions was analyzed for events containing two leptons $(e$ or $\ensuremath{\mu}),$ two or more jets, and missing transverse energy. Assuming the minimal supergravity model, with ${A}_{0}=0$ and $\ensuremath{\mu}l0,$ various thresholds were employed to optimize the search. No events were found beyond expectation from the background. We set a lower limit at the 95% C.L. of 255 $\mathrm{GeV}{/c}^{2}$ for equal mass squarks and gluinos for $\mathrm{tan}\ensuremath{\beta}=2,$ and present exclusion contours in the ${(m}_{0}{,m}_{1/2})$ plane for $\mathrm{tan}\ensuremath{\beta}=2$--6.

Ratios of multijet cross sections in pp̄ collisions at √s= 1.8 TeV

Abstract: We report on a study of the ratio of inclusive three-jet to inclusive two-jet production cross sections as a function of total transverse energy in p (p) over bar collisions at it center-of-mass energy roots = 1.8 TeV, using data collected with the DO detector during the 1992-1993 run of the Fermilab Tevatron Collider. The measurements are used to deduce preferred renormalization scales in perturbative O(alpha (3)(s)) QCD calculations in modeling soft-jet emission.

Measurement of the angular distribution of electrons from [Formula Presented] decays observed in [Formula Presented] collisions at [Formula Presented] TeV

Abstract: We present the first measurement of the electron angular distribution parameter α 2 in W→eν events produced in proton-antiproton collisions as a function of the W boson transverse momentum. Our analysis is based on data collected using the DO detector during the 1994–1995 Fermilab Tevatron run. We compare our results with next-to-leading order perturbative QCD, which predicts an angular distribution of (1±α 1 cosθ ∗ +α 2 cos 2 θ ∗ ), where θ ∗ is the polar angle of the electron in the Collins-Soper frame. In the presence of QCD corrections, the parameters α 1 and α 2 become functions of p T W , the W boson transverse momentum. This measurement provides a test of next-to-leading order QCD corrections which are a non-negligible contribution to the W boson mass measurement.